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Cardiovascular Block: Week 7 > The Common Trisomies (Chromosome Disorders 1) > Flashcards

The Common Trisomies (Chromosome Disorders 1) Flashcards

1
Q

What proportion of spontaneous miscarriages are due to chromosome abnormalities?

A

~50%

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2
Q

What proportion of stillbirths are due to chromosome abnormalities?

A

5%

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3
Q

What proportion of mental retardation is due to chromosome abnormalities?

A

10%

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4
Q

What proportion of live births are found to have significant chromosome abnormalities?

A

0.5-1%

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5
Q

Chromosome abnormalities may be divided into what two categories?

A
  1. Numerical

2. Structural

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6
Q

What types of structural chromosome disorders are there?

A
  • Translocations
  • Deletions
  • Duplications
  • Insertions
  • Inversions
  • Ring Chromosomes
  • Isochromosomes
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7
Q

What are the three types of translocations?

A
  1. Balanced
  2. Unbalanced
  3. Robertsonian
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8
Q

What does a deletion result in?

A

Creates a partial monosomy (when pieces of chromosomes are missing)

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9
Q

What does duplication result in?

A

Creates partial trisomy (when pieces of chromosomes are added)

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10
Q

What is a reciprocal translocation?

A

Balanced translocation,

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11
Q

What is the result of a balanced translocation in an individual?

A

For the carrier, there is no loss or addition of genetic material.
- Phenotypically expected to be normal

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12
Q

What may occur in the offspring of an individual with a balanced translocation?

A

Offspring may be at risk to inherit an unbalanced chromosome complement
- expected to exhibit an abnormal phenotype

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13
Q

What are the consequences of a duplication / deletion?

A

The consequences of a duplication or deletion are determined by the size of the involved segment, the number and type of genes involved and on occasion by the breakpoint.
- Not all deletions / duplications are “pathogenic” some are thought to be benign variants and are not thought to have significant phenotypic consequences.

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14
Q

What are the two types of numerical chromosomal abnormalities?

A
  1. Polyploidy

2. Aneuploidy

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15
Q

What are the two types of aneuploidy?

A
  1. Trisomy

2. Monosomy

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16
Q

What is trisomy?

A

“Too many” chromosomes - 47 chromosomes

e.g. Trisomy 13, 18, 21

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17
Q

What is monosomy?

A

“Too few” chromosomes - 45 chromosomes

e.g. Turner syndrome

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18
Q

What is polyploidy?

A

An “extra set” of chromosomes - 69 chromosomes

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19
Q

What are the majority of chromosome abnormalities due to?

A

Non-disjunction

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20
Q

What proportion of Trisomy 13 pregnancies result in spontaneous abortion?

A

95%

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21
Q

What proportion of Trisomy 18 pregnancies result in spontaneous abortion?

A

95%

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22
Q

What proportion of Trisomy 21 pregnancies result in spontaneous abortion?

A

80%

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23
Q

What proportion of Monosomy X pregnancies result in spontaneous abortion?

A

98%

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24
Q

What is the most common genetic cause of intellectual disability worldwide?

A

Down Syndrome (Trisomy 21)

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25
What causes an increased risk of Down Syndrome?
Increase risk with increased maternal age: - Age 25 = 1/1350 - Age 40 = 1/100 - Age 45 = 1/30
26
Which ethnic group is at greatest risk for Down Syndrome?
All ethnic groups are equally affected
27
What are the three mechanisms by which Down Syndrome may be caused?
1. Non-dysjunction (95%) 2. Translocation (4%) 3. Mosaicism (1%)
28
What craniofacial abnormalities are seen in Down Syndrome?
- flat facial profile and nasal bridge - bradycephaly - epicanthic folds - upslanted eyes - protruding tongue (less frequent in African patients) - small, low set ears
29
What CNS abnormalities are seen in Down Syndrome?
- hypotonia | - global developmental delay / intellectual disability (Ave IQ 45-48)
30
What limb abnormalities are seen in Down Syndrome?
- single palmar crease - clinodactyly - sandle-gap - bradydactyly
31
What proportion of Down Syndrome patient's have cardiac abnormalities?
40-50%
32
What cardiac abnormalities are seen in Down Syndrome?
- AVSD (40% - one of the commonest) - VSD - ASD - PDA - Tetralogy of Fallot
33
What other abnormalities are seen in Down Syndrome?
1. GIT (duodenal atresia, Hirschprungs disease) 2. Visual problems 3. Short stature 4. Undescended testes, small penis
34
What are some of the complications of Down Syndrome?
- Atlanto-axial instability - Recurrent infections = conductive hearing loss - Cataracts - Transient neonatal 'leukemia' - ALL (20x greater risk) - Hypothyroidism (20-40%) due to antibodies - Alzheimer Disease (8% by 49 years; 75% by 60 years)
35
What is the life expectancy of Down Syndrome patients?
Depends on where you live, first world kids live a lot longer.
36
What can be used to diagnose Down Syndrome?
1. Chromosome analysis | 2. PCR Aneuploidy Screen (QF-PCR)
37
What are the recurrence risks for Down Syndrome in Non-dysjunction (<35 years)?
1%
38
What are the recurrence risks for Down Syndrome in Non-dysjunction (>35 years)?
Age related risk
39
What are the recurrence risks for Down Syndrome with a maternal translocation carrier?
10-15%
40
What are the recurrence risks for Down Syndrome with a paternal translocation carrier?
1-3%
41
What are the recurrence risks for Down Syndrome with a maternal translocation carrier, if the father is a 21q21q carrier?
100%
42
What should be done medically to treat Down Syndrome?
1. Annual thyroid function tests 2. Growth monitoring 3. Treat infections / other complications 4. Surgery may be necessary: cardiac, GIT 5. Neurodevelopmental interventions 6. Psychosocial support and genetic counseling
43
What growth charts should be used for Down Syndrome patients?
Normal growth charts (no longer use Down's charts)
44
What should be done for the neurodevelopmental management of Down Syndrome patients?
1. Annual hearing / vision assessments 2. Physio / OT / speech therapy 3. Remedial schooling
45
What is Patau Syndrome?
Trisomy 13
46
What is the prevalence of Patau syndrome?
1/5000 live births, 2% of miscarriages
47
What are the three genetic causes of Patau syndrome?
1. Non-dysjunction (75%) 2. Robertsonian translocation (20%) 3. Mosaicism (5%)
48
What increases the risk of Patau syndrome?
Maternal age related risks
49
What can be seen in a fetus with Patau syndrome?
Antenatal abnormalities - 90% should be detected on ultrasound evaluation
50
What are the features of Patau syndrome at birth?
- scalp defects (50%) - central cleft lip, cleft palate - bulbous nose, post-axial polydactyly - polycystic kidneys
51
What is the life expectancy of an infant with Patau syndrome?
- 85% die in the 1st year | - rarely survive >3 years
52
What is Trisomy 18?
Edwards Syndrome
53
What is the prevalence of Edward's Syndrome?
1/5000 live births, 3% of miscarriages
54
What are the three causes of Edward's Syndrome?
1. Non-dysjunction trisomy (85%) 2. Translocation (5%) 3. Mosaicism (10%)
55
What increases the risk of Edward's Syndrome?
Maternal age related risks
56
What are some of the features of Trisomy 18?
- Often significant IUGR - Increased incidence of congenital anomalies: cardiac, renal, CNS - Microcephaly, micrognathia - Overlapping fingers - Limb abnormalities - Rocker bottom feet
57
What can be done to prevent aneuploidy at a primary prevention level?
Antenatal care, family planning, AMA counseling
58
What can be done to prevent aneuploidy at a secondary prevention level?
Screening for aneuploidy, fetal ultrasound assessments, invasive prenatal testing, TOP
59
What can be done to prevent aneuploidy at a tertiary prevention level?
Reducing complications; surgical intervention, remedial intervention
60
What is the difference in tone abnormalities between Trisomy 21 and Trisomy 18?
Trisomy 21 = hypotonic | Trisomy 18 = hypertonic

Cardiovascular Block: Week 7 (5 decks)

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